Electrical load imbalance detection and protection apparatus

Abstract

The apparatus includes three electrodes housed in a single enclosure which is filled with a gas. A first one of the electrodes is connected to the junction of a load and a fuse. A second one of the electrodes is connected to an intermediate point of the load, which intermediate point separates the load into two normally equal impedance segments. A third one of the electrodes is connected to the other end of the load. When either of the impedances of the two segments of the load changes sufficiently to cause a breakdown voltage between either the first and second electrodes or between the second and third electrodes to be exceeded, current flows between the first and third electrode thereby short-circuiting the load and causing the fuse to break.

What is claimed is: 
     
       1. An apparatus for providing a short-circuit in electrically parallel connection with a load, the load having a first impedance segment defined between a first end of the load and an intermediate point of the load and further having a second impedance segment defined between a second end of the load and the intermediate point, when the load is connected to an energy source and has a sufficient impedance change in either the first impedance segment or the second impedance segment, said apparatus comprising: a first electrode having an end electrically connectible to the first end of the load;   a second electrode, spaced from said first electrode, having an end electrically connectible to the intermediate point of the load so that said first and second electrodes have a first voltage established therebetween when a current flows through the first impedance segment and said first and second electrodes are connected to the first impedance segment, said first voltage being responsive to the impedance of the first impedance segment;   a third electrode, spaced from said first and second electrodes, having an end electrically connectible to the second end of the load so that said second and third electrodes have a second voltage established therebetween when a current flows through the second impedance segment and said second and third electrodes are connected to the second impedance segment, said second voltage being responsive to the impedance of the second impedance segment;   a housing having a hollow interior in which said first, second and third electrodes are disposed; and   wherein a current flows between said first and third electrodes when either said first voltage or said second voltage exceeds a predetermined value.   
     
     
       2. An apparatus as defined in claim 1, wherein each of said first, second and third electrode has an outer surface on which barium and barium oxide are disposed. 
     
     
       3. An apparatus for providing a short-circuit in electrically parallel connection with a load, the load having a first resistive segment defined between a first end of the load and an intermediate point of the load and further having a second resistive segment defined between a second end of the load and the intermediate point, when the load is connected to an energy source and has a sufficient resistive change in either the first resistive segment or the second resistive segment, said apparatus comprising: a first electrode having an end electrically connectible to the first end of the load;   a second electrode, spaced from said first electrode, having an end electrically connectible to the intermediate point of the load, said first and second electrodes having a predetermined breakdown voltage;   a third electrode, spaced from said first and second electrodes, having an end electrically connectible to the second end of the load, said second and third electrodes having a predetermined breakdown voltage;   a housing having a hollow interior in which said first, second and third electrodes are disposed; and   wherein a current flows between said first and third electrodes to provide the short-circuit in electrically parallel connection with the load when said electrodes are connected to the load and either the breakdown voltage of said first and second electrodes or the breakdown voltage of said second and third electrodes is exceeded by a voltage established by a current flowing through the first resistive segment or the second resistive segment.   
     
     
       4. An apparatus as defined in claim 3, further comprising a gas disposed in said hollow interior of said housing. 
     
     
       5. An apparatus as defined in claim 3, wherein each of said first, second and third electrodes has an outer surface on which barium and barium oxide are disposed. 
     
     
       6. An apparatus as defined in claim 3, wherein: said first and second electrodes have a first voltage established therebetween when said first and second electrodes are connected to the load and a current from the energy source flows through the first resistive segment;   said second and third electrodes have a second voltage established therebetween when said second and third electrodes are connected to the load and a current from the energy source flows through the second resistive segment;   said first and second voltages are equal when said first and second resistive segments have equal resistances; and   said first and second voltages are unequal when said first and second resistive segments have unequal resistances.   
     
     
       7. An apparatus as defined in claim 6, wherein: said first voltage is greater than said second voltage when the resistance of the first resistive segment is greater than the resistance of the second resistive segment; and   said first voltage is less than said second voltage when the resistance of the first resistive segment is less than the resistance of the second resistive segment.   
     
     
       8. An apparatus as defined in claim 6, wherein each of said first, second and third electrodes has an outer surface on which barium and barium oxide are disposed. 
     
     
       9. An apparatus as defined in claim 8, further comprising a gas disposed in said hollow interior of said housing. 
     
     
       10. An apparatus for deactivating an electric blanket when a resistive heating element of the electric blanket presents an abnormal load to an energy source to which the resistive heating element, in series with a fuse, is connectible, said apparatus comprising: a glow lamp including a first electrode, a second electrode, and a third electrode;   first connector means for electrically connecting said first electrode to a first end of the resistive heating element, said first end being the end which is electrically connected in series to the fuse;   second connector means for electrically connecting said third electrode to a second end of the resistive heating element opposite said first end thereof; and   third connector means for electrically connecting said second electrode to the resistive heating element intermediate said first and second ends thereof, said intermediate connection dividing the resistive heating element into a first resistive segment and a second resistive segment so that said first resistive segment normally has a resistance equal to a resistance of said second resistive segment.   
     
     
       11. An apparatus as defined in claim 10, wherein said third connector means includes a resistor. 
     
     
       12. An apparatus as defined in claim 10, wherein: said resistive heating element includes: a first electrical conductor defining said first resistive segment and having a first end defining said first end of said resistive heating element and further having a second end; and   a second electrical conductor defining said second resistive segment and having a first end defining said second end of said resistive heating element and further having a second end; and     said third connector means includes: a first resistor having a first end electrically connected to said second electrode and further having a second end electrically connected to said second end of said first electrical conductor; and   a second resistor having a first end electrically connected to said second electrode and said first end of said first resistor and further having a second end electrically connected to said second end of said second electrical conductor.     
     
     
       13. An apparatus as defined in claim 10, wherein each of said first, second and third electrodes is constructed to pass an electrical current having a magnitude large enough to cause the fuse to provide an open circuit. 
     
     
       14. An apparatus as defined in claim 13, wherein each of said first, second and third electrodes includes a surface portion comprising barium and barium oxide. 
     
     
       15. An apparatus as defined in claim 10, wherein each of said first, second and third electrodes includes a surface portion comprising barium and barium oxide. 
     
     
       16. An apparatus as defined in claim 15, wherein said third connector means includes a resistor. 
     
     
       17. An apparatus as defined in claim 15, wherein: said resistive heating element includes: a first electrical conductor defining said first resistive segment and having a first end defining said first end of said resistive heating element and further having a second end; and   a second electrical conductor defining said second resistive segment and having a first end defining said second end of said resistive heating element and further having a second end; and     said third connector means includes: a first resistor having a first end electrically connected to said second electrode and further having a second end electrically connected to said second end of said first electrical conductor; and   a second resistor having a first end electrically connected to said second electrode and said first end of said first resistor and further having a second end electrically connected to said second end of said second electrical conductor.     
     
     
       18. An apparatus as defined in claim 10, wherein said glow lamp becomes electrically conductive and passes current between said first and third electrodes when the resistance of said first resistive segment is sufficiently different from the resistance of said second resistive segment so that a voltage having an effective magnitude greater than a predetermined voltage value is applied either between said first and second electrodes or between said second and third electrodes. 
     
     
       19. An apparatus as defined in claim 18, wherein the fuse provides an open circuit, thereby deactivating the electric blanket, when said current passing between said first and third electrodes has an effective magnitude greater than a predetermined current value. 
     
     
       20. An apparatus for preventing a primary impedance load from conducting too much current when the primary impedance load is connected to an energy source, said apparatus comprising: a fuse having a first end connected to a first end of the primary impedance load and having a second end connectible to a first end of the energy source;   connector means for connecting a second end of the primary impedance load to a second end of the energy source; and   a glow lamp including: a first electrode connected to said first end of the primary impedance load;   a second electrode connected to said primary impedance load at a central impedance locus thereof, said central impedance locus dividing said primary impedance load into two segments normally having equal impedances;   a third electrode connected to said second end of the primary impedance load; and   wherein a first one of said two segments of the primary impedance load establishes a first voltage between said first and second electrodes when a current flows through the primary impedance load and a second one of said two segments of the primary impedance load establishes a second voltage between said second and third electrodes when a current flows through the primary impedance load and further wherein a short-circuit current flows between said first and third electrodes when either said first voltage or said second voltage exceeds a predetermined value.     
     
     
       21. An apparatus as defined in claim 20, wherein said connector means includes a resistor disposed between said second end of the primary impedance load and said second end of the energy source. 
     
     
       22. A method of detecting an abnormal electrical load and of providing an electrical short-circuit in electrical parallel to the abnormal electrical load, comprising: connecting a first electrode of a three-electrode glow lamp to a first end of the electrical load;   connecting a second electrode of said glow lamp to an intermediate locus of the electrical load so that a first voltage is established between said first and second electrodes when a current flows through the electrical load, said first voltage being proportional to the impedance of the portion of the electrical load between said first end and said intermediate locus thereof; and   connecting a third electrode of said glow lamp to a second end of the electrical load so that a second voltage is established between said second and third electrodes when a current flows through the electrical load, said second voltage being proportional to the impedance of the portion of the electrical load between said intermediate locus and said second end thereof, wherein the electrical short-circuit is provided between said first and third electrodes when either said first voltage or said second voltage exceeds a predetermined value.